1. Technical Field
The present invention relates to an electronic timepiece with an internal antenna.
2. Related Art
Electronic timepieces that receive signals frompositioning information satellites such as GPS (Global Positioning System) satellites to display time accurately are known from the literature. Such electronic timepieces have a ring-shaped antenna for receiving radio signals frompositioning information satellites. See, for example, JP-A-2009-168656 or Japan Patent 3982918.
A movement for displaying analog time, a case that houses the movement, a cover member that covers the face side of the movement, a ground plane disposed between the cover member and the movement, and a ring-shaped antenna disposed on the outside of the ground plane between the ground plane and the cover member are disclosed in JP-A-2009-168656, thereby assuring both a feeling of good quality and good antenna performance at the same time.
A ring-shaped antenna comprising a C-shaped loop element that is disposed inside the case of a wristwatch and receives circularly polarized waves is disclosed in Japan Patent 3982918. The circumferential length of the antenna is approximately equal to one wavelength of the RF signal after wavelength shortening by the dielectric. The technology taught in Japan Patent 3982918 enables reducing the size of the antenna by means of wavelength shortening so that a loop antenna for receiving GPS satellite signals (1 wavelength=19 cm) can be fit inside the outside case member of a wristwatch.
Technology using a parasitic element not connected to a circuit has also been used to efficiently receive circularly polarized waves from GPS satellites. More specifically, the parasitic element is disposed near the antenna element that is fed, and impedance is improved by electromagnetically coupling the parasitic element to the antenna element and lowering the resonance frequency. GPS signal reception performance can thus be improved by adjusting the resonance frequency to the GPS satellite signal, for example.
However, when such a parasitic element is used with a ring-shaped antenna as disclosed in JP-A-2009-168656 and Japan Patent 3982918, the parasitic element will be located near the case because the antenna element is disposed near the case, which is made of a conductive material. As a result, the parasitic element will be affected by the conductive case members, the antenna performance of the parasitic element cannot be assured, and signal reception sensitivity drops.